The present invention relates, generally, to implantable infusion devices having reservoirs and reservoir structures for such devices and, in preferred embodiments, to such devices and reservoirs configured to minimize the device thickness dimension, including methods of making and using the same.
Implantable infusion devices are typically used to deliver an infusion media, such as a medication, to a patient. Such devices are typically designed to be implanted in a patient""s body, to administer an infusion media to the patient at a regulated dosage.
Because implantable infusion devices are designed to be implanted in the patient""s body, the dimensions of such devices can have an impact on the determination of the location on the body at which devices may be implanted, the level of comfort of the implant patient and the external appearance of the implant site. Typically, a device with relatively small dimensions and, in particular, a relatively small thickness dimension, will provide greater flexibility in the choice of location on the patient""s body to place the implant and will minimize patient discomfort and minimize noticeable protrusions at the implant site. Accordingly, there is a need in the industry for implantable infusion device configurations with minimized overall dimensions and, in particular, with minimized thickness dimensions.
However, the volume of infusion media that a given device is capable of containing (also referred to as the volume capacity of the device) may be dependent, at least in part, on the dimensions of the device. Typically, smaller device designs have smaller volume capacities and, thus, require more frequent re-filling or replacement operations, as compared to larger devices. Thus, there is often a trade-off between benefits achievable with reductions in device dimensions (size reductions) and benefits of increasing or maintaining the volume capacity of the device. Accordingly, there is a further need in the industry for implantable infusion device configurations with improved volume capacities or which have minimized device dimensions with little or no reduction in volume capacity.
Typical implantable infusion devices include a generally disc-shaped housing having a diameter dimension and a thickness dimension. The thickness dimension of the device is dependent, at least in part, upon the relative placement of device components and the thickness dimensions of the device components. Such devices typically include a reservoir located within the housing for holding a volume of an infusion medium, for example, a liquid medication. Such devices also typically include an inlet for receiving infusion medium into the reservoir to fill or re-fill the reservoir, for example, from a hollow needle, such as a syringe needle.
In addition, implantable infusion devices may include a driving mechanism, such as a pump, for controlling the flow of infusion medium from the reservoir to the patient, through an outlet in the housing, either on a continuous basis, at scheduled or programmed times or in response to signals from a sensor or other signal source. Other devices include pressurized gas sources for driving infusion medium from the reservoir. Each of those components define a thickness dimension which, depending upon their placement on the device, may affect the overall thickness dimension of the implantable infusion device.
Example implantable infusion devices are described in U.S. Pat. No. 5,527,307, U.S. Pat. No. 5,514,103 and U.S. Pat. No. 5,176,644, each to Srisathapat et al. (and assigned to Minimed Technologies, Ltd.), U.S. Pat. No. 5,167,633 to Mann et al. (and assigned to Pacesetter Infusion, Ltd,), U.S. Pat. No. 4,697,622 to Swift (assigned to Parker Hannifin Corporation) and U.S. Pat. No. 4,573,994 to Fischell et al. (assigned to The Johns Hopkins University), each of which is incorporated herein by reference. Each of the above-cited patents describes an implantable infusion device which includes a generally disc-shaped housing containing a reservoir, a driving mechanism or pump, an inlet, an outlet and an electronic circuit for controlling the operation of the driving mechanism or pump.
With reference to the drawings in each of the above-cited patents, a significant portion of the thickness dimension of the illustrated implantable infusion devices is composed of the reservoir in those devices. For example, several of the above-cited patents describe reservoirs composed of a flexible bag within a medication chamber. One example is shown in FIGS. 7-10 of U.S. Pat. No. 5,176,644, where a flexible bag or sack 228 is formed of interconnected sheets of Halar film or the like. As illustrated, about one-half of the overall thickness dimensions of such devices is composed of the medication chamber and bag structure. The bag is filled with a pressure fluid that expands and contracts to inversely vary the volume of the portion of the medication chamber outside of the bag and to provide a relatively constant pressure on the medication in the medication chamber, as the medication is dispensed. However, in the pressurized bag arrangement, a repetitive compression and expansion of the flexible bag, as may occur after multiple fill and re-fill operations, can tend to wear and/or fatigue the bag and, possibly tear or otherwise impair the operation of the bag. In addition, plastics and Halar films can tend to allow infusion medium and/or propellant to diffuse through the bag material.
Other implantable infusion device configurations, such as shown in the ""622 patent to Swift, employ a moveable diaphragm that cooperates with the lower shell of the device to define a pressurant chamber filled with gas pressurant and cooperates with an internal wall (base) to define a reservoir. The diaphragm shown in the Swift patent has multiple convolutions or waves which apparently are configured to match corresponding grooves and ridges formed in the lower shell and in the internal wall (or base). However, the groove and ridge configuration of the shell and internal wall tend to increase the thickness of the shell and internal wall, without providing a corresponding increase in volume capacity. In addition, multiple convolutions can increase the stiffness of the diaphragm and, thus, require a greater amount of energy to move the diaphragm. Furthermore, convolutions may provide additional stress or fatigue points on the diaphragm.
Yet other implantable infusion device configurations employ an expandable bellows structure secured within a chamber and filled with a pressurized gas. In such arrangements, one end of the bellows structure is secured to a wall of the chamber, while the other end is allowed to move toward and away from the opposite wall of the chamber, as gas outside of the bellows expands and contracts, as the bellows expands or contracts. The volume within the bellows defines a reservoir for the infusion medium. Because the bellows structure inherently includes multiple creases or joints, a significant portion of the volume of the reservoir tends to be unusable. In addition, such bellows structures tend to require relatively complex structures of welded plates and multiple welded joints, which can increase the cost and adversely affect the reliability of the infusion device. Furthermore, infusion media may tend to stagnate within the multiple creases or joints of the bellows structure, which may lead to aggregation, statification and chemical degradation.
Thus, there is a need for new and improved implantable infusion device configurations and reservoir configurations having reduced thickness dimensions and/or improved volume capacities, without compromising the operational life, reliability and efficiency of the device.
The present invention relates generally to implantable infusion devices. Particular embodiments relate to reservoir structures for such devices and methods of making and using the same.
Embodiments of the present invention employ reservoir configurations that reduce the thickness requirements of the device for a given longitudinal dimension, while maintaining similar volume capacities as prior reservoirs. In addition, reservoir configurations according to embodiments of the invention allow multiple dispensing and fill or re-fill operations, with reduced risk of damage to the reservoir components. In this manner, an implantable device may be formed with a relatively thin housing, and yet provide the capacity for containing at least the same, or greater, volumes of infusion medium, as compared to prior reservoir configurations, without compromising the operational life span of the device.
An implantable infusion device according to an embodiment of the invention includes a generally disc-shaped housing that is made from a biocompatible material or is appropriately coated with a biocompatible material to obtain a desired biocompatibility. The housing contains a reservoir for holding a volume of infusion medium, such as, but not limited to, a medication to be administered to the patient.
The housing has an outlet through which the infusion medium may be expelled. The reservoir is coupled in fluid flow communication with the outlet. In some embodiments, a drive mechanism may be coupled in fluid flow communication with the reservoir, to drive infusion fluid out of the reservoir, through the outlet. In other embodiments, fluid may flow or be drawn from the reservoir by other suitable means.
The reservoir defines a chamber that contains at least one flexible diaphragm. Each diaphragm has an outer peripheral edge fixed within the chamber, a convolution adjacent the peripheral edge and a generally smooth central portion that is free to flex within the chamber, wherein the convolution enhances the flexibility of the diaphragm. A ring is provided in alignment with the peripheral edge of each diaphragm. The ring has a central opening that is aligned with the convolution and central portion of each diaphragm, to allow the diaphragm to flex within the ring. In this manner, the volume on one side of each diaphragm may be varied to correspond to a varying volume of infusion medium. Similarly, the volume within the reservoir chamber on the other side of the diaphragms is varied as the diaphragms flex, to correspond to the expansion and contraction of a propellant medium within the reservoir. In an alternative embodiment, the diaphragm edges may be free-floating within the chamber.
The above arrangements allow for a relatively thin configuration of a reservoir chamber containing one or more diaphragms, yet further allows for the storage of infusion medium within a significant portion of the reservoir chamber, with little or no unused space within the reservoir chamber. In addition, the configuration allows for multiple flexures of the diaphragm, with reduced risk of damage to the diaphragms.